Regulation of gene expression by GH is a focus to understand the mechanism of action of GH. In 3T3-F442A cells, GH induces c-fos transcription, via the serum response element (SRE). We are investigating involvement of transcription factors associated with the SRE and with the SIF-binding sequence in GH action. Other approaches include studying signaling between GH receptors and c-fos tyrosine kinase, and assessment of GH action in cells expressing anti-sense c- fos.